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Although northern wheatgrass (Agropyron dasystachyum (Hook.) Scrihn.) is a dominant or co-dominant species that decreases under grazing in northern Mixed Prairie, little is known about its response to herbage removal at different times during the growing season. The objective of this research was to determine the effects of defoliation on the tiller production and survival of this native perennial on a clayey range site in mixed prairie in south-central Saskatchewan. Vegetation was subjected to a factorial experiment with an initial defoliation in early-May, June, July, or August and repeated at 2-or L-week intervals until mid-September in the same plots for 3 years. An undefoliated control was also included. On average defoliation enhanced tillering (71%) and survival relative to the control, and tiller recruitment was greatest during June and September 1989. Generally tiller survival decreased as the date of emergence in the growing season was delayed. Numbers of tillers emerging was positively correlated with soil water (r=O.77). Some tillers of northern wheatgrass lived 5 years. The 2-and 6-week intervals of defoliation had little influence on tiller survival, but initiating defoliation near the time of tiller emergence reduced survival whereas delaying defoliation until August increased their survival. Increased tillering may be an adaptive feature enabling northern wheatgrass to tolerate defoliation by re-establishing lost photosynthetic area and maintaining or even increasing basal area. Thus, once released from grazing it may rapidly increase phytomass production in a relatively short time. Delaying grazing until August will maximize tiller survival of northern wheatgrass.

In South China, certain problems exist in some of aquaculture pond ecosystems, where the concentrations of total phosphorus are high in the sediment but the concentrations of phosphate are low in the overlying water. It is very important and necessary to isolate and screen some phosphate-solubilizing bacteria (PSB) that can adapt to the pond environment for enhancing the utilization of phosphorus in the aquaculture systems. To reach the objective, one PSB, named g6, was isolated using modified Pikovskaya and Pikovskaya medium. By 16S rDNA sequencing analysis and BIOLOG auto-identification system, this strain was identified as Pantoea stewartii subsp. stewartii. After 144 h strains cultivation in liquid National Botanical Research Institute's phosphate growth medium, its activity resulted in accumulations of soluble phosphate 543 mg l -1 . Based on the aquaculture pond ecosystems in South China, effects of temperature, salinity, and pH on g6's growth were also conducted under indoor culture conditions. Results indicated that Pantoea stewartii subsp. stewartii g6 could tolerate wide range of temperature 15-35°C, salinity 5-35%, and initial pH 6-10. The results showed that g6 had high solubilization efficiency in vitro and could be expected to adapt well to different aquaculture pond environments, based on culture results.

BackgroundImproving the efficiency of animal production is a relentless pursuit of ruminant producers. Energy utilization and partition can be affected by dietary composition and nutrient availability. Furthermore, the liver is the central metabolic intersection in cattle. However, the specific metabolic changes in the liver under conditions of limit-feeding remain unclear and require further study. The present study aimed to elucidate the effects of a wide range of dietary forage:concentrate ratios (F:C) on energy utilization, and identify potential changes in molecular metabolism by analyzing hepatic transcriptional profiles. Twenty-four half-sib Holstein heifers were fed four F:C diets (20:80, 40:60, 60:40, and 80:20 on a dry matter basis), with similar intake levels of metabolizable energy (ME) and crude protein. Liver biopsy samples were obtained and RNA sequencing was conducted to identify the hepatic transcriptomic changes. Moreover, the ruminal fermentation profiles, growth characteristics, and levels of metabolites in the liver and plasma of the heifers were monitored.ResultsThe proportion of acetate showed a linear increase (P < 0.01) with increasing dietary forage levels, whereas the proportion of propionate showed a linear decline (P ≤ 0.01). Lower levels of average daily gain and feed efficiency (P < 0.01) were observed in heifers fed high levels of forage, with a significant linear response. Using the Short Time-series Expression Miner software package, the expression trends of significant differentially expressed genes (DEGs) were generally divided into 20 clusters, according to their dynamic expression patterns. Functional classification analysis showed that lipid metabolism (particularly cholesterol and steroid metabolism which were in line with the cholesterol content in the liver and plasma) was significantly increased with increasing dietary forage levels and slightly reduced by the 80% forage diet. Nine DEGs were enriched in the related pathways, namely HMGCS1, HMGCR, MSMO1, MVK, MVD, IDI1, FDPS, LSS, and DHCR7.ConclusionsThe ruminal fermentation and feed efficiency results suggest that different mechanisms of energy utilization might occur in heifers fed different F:C diets with similar levels of ME intake. Increased cholesterol synthesis from acetate might be responsible for the reduced efficiency of energy utilization in heifers fed high-forage diets.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4529-9) contains supplementary material, which is available to authorized users.